The present invention relates to a device for continuous regulation of the gas flow rate processed by a reciprocating compressor.
As is known, a reciprocating compressor is an operating machine which returns a compressible fluid (gas or vapour), at a pressure greater than that at which it received the fluid.
The reciprocating compressor operates with at least one cylinder, which communicates at appropriate moments with a delivery environment or with a suction environment; the fluid is sucked from the suction environment, subsequently compressed, and finally discharged to the exterior.
In this context, the need to reduce the flow rate of the gases processed by a reciprocating compressor in relation to its maximum value (100%, or full load), without varying the number of reciprocations, is a requirement which occurs quite frequently.
In particular, the variation of gas flow rate in reciprocating compressors can take place in the following manners: firstly discontinuously, which means with the possibility of being stabilised only at predetermined xe2x80x9cstepsxe2x80x9d, or values of flow rate.
Secondly, the variation of gas flow rate can take place continuously, i.e. with the possibility of covering any value as required, within the field of regulation.
With particular reference to the state of the art, it should be noted that at present, the flow rate of reciprocating compressors is regulated by means of the following systems.
The first known system comprises recirculation of the flow rate by means of a by-pass valve; in fact, this system consists of having the flow rate, which is in excess of that required, recirculated from the delivery of the compressor to the point of suction, by means of the assistance of a regulation valve.
However, this system has the disadvantage that all the energy expended must be dissipated, in order to compress the recirculated flow.
A second system according to the known art consists of choking the effects, understood as the action of one or two surfaces of the piston, by means of use of appropriate valve lifters.
In fact, in this known system, the regulation is carried out by deactivating one or more cylinders of the compressor, thus mechanically preventing the suction valves from reclosing during the phase of compression of the cylinder, by means of some devices which are known as valve lifters.
By this means, the compressed gas flows back from the cylinder to the suction line, throughout the compression phase.
However, there is a loss of energy during the phase of reflux of the gases via the suction valve.
In addition, the flow rate can be regulated only in steps (typically with values of 50%, 75% and 100% of the flow rate), and thus, in most cases, a by-pass must also be added between the points of suction and delivery, if it is wished to obtain more accurate regulation of the flow rate.
A third system according to the known art is based on the concept of delay in closure of the suction valves.
The system consists of delaying closure of the suction valves during the compression phase, by acting mechanically on the said valve lifters.
To summarise, during the compression phase, part of the gas which is present in the cylinder flows back along part of the path of the piston, in the suction line; the delay in closure of the suction valves thus permits continuous regulation of the flow rate.
However, the main disadvantage of this system is the dissipation of energy, caused by the reflux of the gases which occurs through the suction valve.
Finally, according to a fourth system, there is insertion of additional dead spaces.
The system consists of additional inhibiting volumes, which are provided in the bases of the cylinders.
This permits regulation of the flow rate in steps, in the case of switching on/off, or continuously, if continuous variation of its volume takes place.
In this last case, the dead space consists of a cylinder (in free communication with the compression cylinder), in which there slides a piston, the displacement of which gives rise to variation of the volume of the dead space itself.
By this means, to each position of the piston there corresponds a value of the dead space, and thus a flow rate value.
Owing to the absence of restrictions between the compression cylinder and the inhibiting volume, the energy expended in order to compress the gas which remains in this volume is fully restored in the re-expansion without significant losses.
Continuous activation of the dead spaces makes it possible to adapt the flow rate to the actual requirement, throughout the field of regulation, thus preventing the energy losses which are associated with the recirculation of part of the flow rate by means of a by-pass, volume increaser, or valve closure return.
At present, bases are provided for cylinders, with dead spaces which are variable continuously only by means of manual actuation, by using flywheels which, by means of a manoeuvring screw, position the piston which closes the base of the cylinders.
The object of the present invention is thus to provide a device for continuous regulation of the gas flow rate processed by a reciprocating compressor, which eliminates the above-described disadvantages, thus making it possible to prevent undesirable dissipations of energy.
Another object of the present invention is to indicate a device for continuous regulation of the gas flow rate processed by a reciprocating compressor, which makes it possible to eliminate the said valve lifters.
A further object of the present invention is to indicate a device for continuous regulation of the gas flow rate processed by a reciprocating compressor, which permits total or partial exclusion of the recirculation valves.
Another object of the present invention is to indicate a is device for continuous regulation of the gas flow rate processed by a reciprocating compressor, which is economical, safe, and reliable.
This object and others according to the invention are obtained by a device for continuous regulation of the gas flow rate processed by a reciprocating compressor, wherein the said reciprocating compressor has at least one first compression piston, which is associated with a first cylinder, and can create pressure which is variable over a period of time, and a second piston, which acts inside a second cylinder, which is in free communication with the said first compression cylinder, associated with the said first piston, and which acts on an additional dead space, characterised in that it includes a third fluid mechanics cylinder, which moves the said piston of the dead space, wherein the said third fluid mechanics cylinder is activated by means of a compressed fluid, supplied by means of an independent hydraulic system, in order to obtain continuous variation of the said dead space.
According to a preferred embodiment of the present invention, the hydraulic system has an oil tank, a pump which is activated by an electric motor, an accumulator, and a pair of on-off directional solenoid valves.
According to another preferred embodiment of the present invention, each of the said directional solenoid valves is supplied with a compressed hydraulic fluid obtained from the said hydraulic system.
In addition, the hydraulic system has a filter and a pressure switch, for each of the said on-off directional solenoid valves.
According to another preferred embodiment of the present invention, the said solenoid valves are controlled by means of a regulator, according to a negative feedback signal obtained in the reciprocating compressor.
More particularly, the negative feedback signal is a signal which indicates the delivery pressure or the flow rate processed.
According to a further preferred embodiment of the present invention, the said device includes a pressure or flow-rate transmitter, in order to send the signal to be regulated, to an electronic controller, which, on the basis of a set-point value previously set, in turn sends a control signal to the said on-off directional solenoid valves.
In particular, according to the set point set in the controller, the solenoid valves make compressed oil flow from one of the two sides of the fluid mechanics cylinder, consequently emptying the other side, and give rise to movement of the piston of the additional dead space, all in order to vary the volume of the said additional dead space, until the said transmitter sends to the said controller a signal which coincides with the set point of the said controller.
The transmitter is connected by means of an electric line to the controller, which is connected by means of an electric line to the said on-off directional solenoid valves, which in turn are connected hydraulically by means of a pair of hydraulic lines to the said fluid mechanics cylinder.
The device for continuous regulation of the gas flow rate can be applied to all compressors with pistons of the reciprocating type, whether the machines are monophase or multi-phase.
Further characteristics of the invention are defined in the other claims attached to the present application.
The particular characteristics and advantages of the device according to the present invention, for continuous regulation of the gas flow rate processed by a reciprocating compressor, will become more apparent from the following description of a typical embodiment of it, provided by way of non-limiting example, with reference to the attached schematic drawings,